Controller for vane-type variable timing adjusting mechanism

ABSTRACT

One-way valves ( 30, 31 ) are provided in a hydraulic supply passage ( 28 ) in an advance chamber ( 18 ) and a hydraulic supply passage ( 29 ) in a retard chamber ( 19 ) respectively for preventing reverse flow of oil from each chamber ( 18, 19 ) and drain oil passages ( 32, 33 ) bypassing the one-way valves respectively disposed in the hydraulic supply passages ( 28, 29 ) of the respective hydraulic chambers ( 18, 19 ) are provided to be in parallel therewith. Drain switching valves ( 34, 35 ) are disposed in the respective drain oil passages ( 32, 33 ). A hydraulic control valve ( 21 ) for controlling a hydraulic pressure supplied to the advance chamber ( 18 ) and the retard chamber ( 19 ) includes integrally a drain switching control function ( 38 ) for controlling a hydraulic pressure supplied to the respective drain switching valves ( 34, 35 ). A point where a VCT response speed rapidly changes by switching opening/closing of the drain switching valves ( 34, 35 ) is learned to improve a control characteristic in the vicinity of the rapidly changing point of the VCT response speed.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2006-121419filed on Apr. 26, 2006, the disclosure of which is incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to a controller for a vane-type variablevalve timing adjusting mechanism in which one-way valves are disposed ina hydraulic supply passage of an advance hydraulic chamber and in ahydraulic supply passage of a retard hydraulic chamber respectively forpreventing reverse flow of operating oil from the respective hydraulicchambers.

BACKGROUND OF THE INVENTION

A vane-type variable valve timing adjusting mechanism is, as shown inJP2001-159330A (U.S. Pat. No. 6,330,870B1), adapted in such a mannerthat a housing rotating in a timed relation to a crank shaft of anengine is disposed coaxially with a vane rotor connected to a cam shaftof an intake valve (or exhaust valve) and a plurality ofvane-accommodating chambers formed in the housing respectively aredivided into an advance hydraulic chamber and a retard hydraulic chamberby vanes (blade portions) at the outer periphery of the vane rotor. Inaddition, the hydraulic pressure in each hydraulic chamber is designedto be controlled by a hydraulic control valve to rotate the vane rotorrelative to the housing, so that a displacement angle of the camshaft(cam shaft phase) to the crankshaft is varied to variably control valvetiming.

In such vane-type variable valve timing adjusting mechanism, at the timeof opening/closing the intake valve or the exhaust valve during engineoperating, fluctuations of torque which the camshaft receives from theintake valve or the exhaust valve are transmitted to the vane rotor. Inconsequence, torque fluctuations in the retard direction or in theadvance direction are exerted on the vane rotor. Thereby, when the vanerotor is subjected to torque fluctuations in the retard direction, theoperating oil in the advance hydraulic chamber is to be subjected tosuch pressure as to be pushed out of the advance hydraulic chamber orwhen the vane rotor is subjected to torque fluctuations in the advancedirection, the operating oil in the retard hydraulic chamber is to besubjected to such pressure as to be pushed out of the retard hydraulicchamber. In consequence, in a low-rotation region where pressuressupplied from a hydraulic supply source are low, even when adisplacement angle of the cam shaft is designed to be advanced bysupplying the hydraulic pressure to the advance hydraulic chamber, thevane rotor is, as shown in a dotted line of FIG. 3, pushed back in theretard direction due to the torque fluctuations. As a result, theresponse time to a target displacement angle of the vane rotor islonger.

In order to solve this problem, as shown in JP2003-106115A (U.S. Pat.No. 6,763,791 B2), a one-way valve is disposed in each of a hydraulicsupply passage of an advance hydraulic chamber and a hydraulic supplypassage of a retard hydraulic chamber for preventing reverse flow ofoperating oil from the advance hydraulic chamber or the retard hydraulicchamber. Thereby, as shown in a solid line of FIG. 3, it is consideredthat this one-way valve is adapted to prevent the vane rotor from beingpushed back in the reverse direction to the direction of a targetdisplacement angle during variable valve timing controlling, improvingresponse characteristic of the variable valve timing control.

In the variable valve timing adjusting mechanism, the one-way valve isdisposed in each of the hydraulic supply passage of the advancehydraulic chamber and the hydraulic supply passage of the retardhydraulic chamber (hydraulic introduction line) and also a returningline (hydraulic discharge line) is disposed in parallel to the hydraulicsupply passage of each hydraulic chamber for bypassing the one-wayvalve. As a result, this controller provides a structure where afunction as a line switching valve for opening/closing the returningline of each hydraulic chamber is united to a hydraulic control valve(spool valve) controlling the hydraulic pressure supplied to eachhydraulic chamber. Further, a control current value of the hydrauliccontrol valve is controlled to control the hydraulic pressure suppliedto each hydraulic chamber and at the same time, to control the switchingin opening/closing of the returning line of each hydraulic chamber.Hereby, when the hydraulic pressure in each hydraulic chamber isrequired to be released, this controller is adapted to quickly releasethe hydraulic pressure through the returning line by opening thereturning line of the corresponding hydraulic chamber.

Since an operating characteristic of the variable valve timing adjustingmechanism or the hydraulic control valve, however, has manufacturingvariations, it is difficult to accurately perform both of the hydrauliccontrol of each hydraulic chamber and the switching control of thereturning line simultaneously by using one hydraulic control valve towhich a function of the line switching valve is united. In addition, itis unavoidable that variations in a response characteristic of the vanerotor (relation between a control current value of the hydraulic controlvalve and a response speed of the vane rotor) occur. The variations ofthis response characteristic are the cause of reducing the effect(effect of an improvement in a response characteristic of an advanceoperation in a low hydraulic region) obtained by the one-way valve.

DISCLOSURE OF THE INVENTION

The present invention is made in view of the foregoing problems and anobject of the present invention is to provide a controller for avane-type variable valve timing adjusting mechanism which can perform avariable valve timing control (control for a control current value of ahydraulic control valve) in consideration of manufacturing variations ofthe variable valve timing adjusting mechanism or the hydraulic controlvalve.

In order to achieve the above object, according to an aspect of thepresent invention, each of a plurality of vane accommodating chambersformed in a housing of a vane-type variable valve timing adjustingmechanism is divided into an advance hydraulic chamber and a retardhydraulic chamber by a vane. There is provided a one-way valve disposedin each of a hydraulic supply passage of the advance hydraulic chamberand a hydraulic supply passage of the retard hydraulic chamber in atleast one of the vane accommodating chambers for preventing reverse flowof operating oil from the each hydraulic chamber A drain oil passage isdisposed in parallel to the hydraulic supply passage of the eachhydraulic chamber for bypassing the one-way valve and a hydrauliccontrol valve for controlling a hydraulic pressure supplied to the eachhydraulic chamber has a drain switching control function foropening/closing the drain oil passage of the each hydraulic chamber.Further, there is provided response characteristic learning means forlearning a response characteristic of the variable valve timingadjusting mechanism to a control current value of the hydraulic controlvalve. In this way, the response characteristic of the variable valvetiming adjusting mechanism to the control current value of the hydrauliccontrol valve during engine operating can be learned and therefore, useof the learning value allows realization of a variable valve timingcontrol (control for the control current value of the hydraulic controlvalve) in consideration of manufacturing variations of the variablevalve timing adjusting mechanism or the hydraulic control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a variable valve timing adjustingmechanism and a hydraulic control circuit thereof in an embodiment ofthe present invention.

FIG. 2 is diagrams each explaining a retard operation, a holdingoperation and an advance operation in the variable valve timingadjusting mechanism.

FIG. 3 is a characteristic diagram explaining a difference in VCT(variable valve timing adjusting mechanism) response speed at advanceoperating depending on presence/absence of a one-way valve.

FIG. 4 is a characteristic diagram showing one example of a responsecharacteristic of the variable valve timing adjusting mechanism with aone-way valve.

FIG. 5 is a time chart explaining a first learning method of a rapidlychanging point of a VCT response speed at a retard side.

FIG. 6 is a time chart explaining a second learning method of a rapidlychanging point of a VCT response speed at a retard side.

FIG. 7 is a diagram plotting measurement points of a VCT displacementangle changing amount ΔVCT measured at the first and second learning ofa rapidly changing point of a VCT response speed at a retard side.

FIG. 8 is a time chart explaining a first learning method of a rapidlychanging point of a VCT response speed at an advance side.

FIG. 9 is a time chart explaining a second learning method of a rapidlychanging point of a VCT response speed at an advance side.

FIG. 10 is a diagram plotting measurement points of a VCT displacementangle changing amount ΔVCT measured at the first and second learning ofa rapidly changing point of a VCT response speed at an advance side.

FIG. 11 is a diagram showing one example of a map of a targetdisplacement angle at a normal control time.

FIG. 12 is a time chart explaining a setting method of a targetdisplacement angle at VCT response characteristic learning.

FIG. 13 is a characteristic diagram representing one example of anengine torque increasing/decreasing rate characteristic to a VCTdisplacement angle at a constant throttle opening.

FIG. 14 is a time chart explaining a control example before completinglearning of a VCT response characteristic.

FIG. 15 is a time chart explaining a control example after completinglearning of a VCT response characteristic.

FIG. 16 is a flow chart explaining the process flow in a determinationroutine for a learning execution condition of a VCT responsecharacteristic.

FIG. 17 is a flow chart explaining the process flow in a learningroutine for a VCT response characteristic.

FIG. 18 is a flow chart explaining the process flow in a learningroutine for a VCT response characteristic.

FIG. 19 is a flow chart explaining the process flow in a control routinefor an OCV current.

FIG. 20 is a flow chart explaining the process flow in a calculationroutine for a current value for normal control.

FIG. 21 is a flow chart explaining the process flow in a calculationroutine for a target displacement angle.

FIG. 22 is a schematic diagram showing a variable valve timing adjustingmechanism and a hydraulic control circuit thereof in another embodimentof the present invention.

BEST MODE OF CARRYING OUT THE INVENTION

Hereinafter, embodiments for a best mode of carrying out the presentinvention will be described.

First, a structure of a vane-type variable valve timing adjustingmechanism 11 will be explained with reference to FIG. 1. A housing 12 ofthe variable valve timing adjusting mechanism 11 is clamped and fixed toa sprocket rotatably supported at an outer periphery of a cam shaft inan intake side or an exhaust side (not shown) by bolts 13. Inconsequence, rotation of a crank shaft for an engine is transmittedthrough a timing chain to the sprocket and the housing 12, and thesprocket and the housing 12 rotate in a timed relation to the crankshaft. A vane rotor 14 is accommodated inside the housing 12 so as torotate relative thereto and is clamped and fixed to one end of the camshaft by a bolt 15.

A plurality of vane accommodating chambers 16 for accommodating aplurality of vanes 17 at an outer periphery of the vane rotor 14 so asto rotate in the advance direction or the retard direction relative tothe housing 12 are defined inside the housing 12 and each vaneaccommodating chamber 16 is divided into an advance hydraulic chamber(hereinafter, referred to as “advance chamber”) 18 and a retardhydraulic chamber (hereinafter, referred to as “retard chamber”) 19.

At a state where a hydraulic pressure beyond a predetermined pressure issupplied to the advance chamber 18 and the retard chamber 19, the vane17 is held by the hydraulic pressures in the advance chamber 18 and theretard chamber 19 to transmit rotation of the housing 12 caused byrotation of the crank shaft to the vane rotor 14 through the hydraulicpressures, thereby rotating the cam shaft integrally with the vane rotor14. During engine operating, the hydraulic pressures in the advancechamber 18 and the retard chamber 19 are controlled by a hydrauliccontrol valve 21 to rotate the vane rotor 14 relative to the housing 12,thereby controlling a displacement angle of the cam shaft (cam shaftphase) to the crank shaft to vary valve timing of an intake valve (orexhaust valve).

In addition, stoppers 22 and 23 for controlling a relative rotationalrange of the vane rotor 14 to the housing 12 are formed at both sideportions of either one of the vanes 17, and the maximum retard positionand the maximum advance position of the displacement angle of the camshaft (cam shaft phase) are restricted by the stoppers 22 and 23. Inaddition, either one of the vanes 17 is provided with a lock pin 24disposed therein for locking a displacement angle of the cam shaft at acertain lock position at engine stopping or the like. This lock pin 24is inserted into a lock hole (not shown) disposed in the housing 12,causing the displacement angle of the cam shaft to be locked at acertain lock position. This lock position is set to a position suitablefor engine startup (for example, substantially intermediate positionwithin an adjustment possible range of a displacement angle of the camshaft).

Oil inside an oil pan 26 (operating oil) is supplied to a hydrauliccontrol circuit of the variable valve timing adjusting mechanism 11through the hydraulic control valve 21 by an oil pump 27. The hydrauliccontrol circuit includes a hydraulic supply oil passage 28 supplying oildischarged from an advance pressure port of the hydraulic control valve21 to a plurality of advance chambers 18 and a hydraulic supply oilpassage 29 supplying oil discharged from a retard pressure port of thehydraulic control valve 21 to a plurality of retard chambers 19.

Further, one-way valves 30 and 31 are disposed in the hydraulic supplyoil passage 28 of the advance chamber 18 and the hydraulic supply oilpassage 29 of the retard chamber 19 for preventing reverse flow of theoperating oil from the respective chambers 18 and 19. In the presentembodiment, the one-way valves 30 and 31 are disposed in the hydrauliccontrol oil passages 28 and 29 of the advance chamber 18 and the retardchamber 19 in the single vane accommodating chamber 16 only. The one-wayvalves 30 and 31 may be disposed in the hydraulic control oil passages28 and 29 of the advance chamber 18 and the retard chamber 19 in each ofa plurality of the vane accommodating chambers 16.

Drain oil passage 32 and 33 for bypassing the one-way valves 30 and 31respectively are disposed in parallel in the hydraulic supply oilpassages 28 and 29 of the respective chambers 18 and 19, and drainswitching valves 34 and 35 are disposed in the drain oil passages 32 and33 respectively. The drain switching valves 34 and 35 respectively areformed of spool valves driven in a closing direction by hydraulicpressure (pilot pressure) supplied from the hydraulic control valve 21.When the hydraulic pressure is not applied, the drain switching valves34 and 35 are held in an opening position. When the drain switchingvalves 34 and 35 are opened, the drain oil passages 32 and 33 areopened, causing functions of the one-way valves 30 and 31 to be stopped.When the drain switching valves 34 and 35 are closed, the drain oilpassages 32 and 33 are closed, causing functions of the one-way valves30 and 31 to be effectively performed. Therefore, the reverse flow ofthe oil from the hydraulic chambers 18 and 19 is prevented, maintainingthe hydraulic pressures in the hydraulic chambers 18 and 19.

The drain switching valves 34 and 35 respectively do not requireelectrical wiring, and are downsized to be incorporated in the vanerotor 14 inside the variable valve timing adjusting mechanism 11,together with the one-way valves 30 and 31. In consequence, the drainswitching valves 34 and 35 are located near the hydraulic chambers 18and 19 respectively and are adapted to open/close the respective drainoil passages 32 and 33 near the respective hydraulic chambers 18 and 19at advance/retard operating in good response.

On the other hand, the hydraulic control valve 21 is formed of a spoolvalve driven by a linear solenoid 36, where an advance/retard hydrauliccontrol valve 37 controlling the hydraulic pressures supplied to theadvance chamber 18 and the retard chamber 19 is integral with the adrain switching control valve 38 switching the hydraulic pressuredriving the drain switching valves 34 and 35 respectively. A currentvalue (control duty) supplied to the linear solenoid 36 of the hydrauliccontrol valve 21 is controlled by an engine control circuit (hereinafterreferred to as “ECU”) 43.

The ECU 43 calculates actual valve timing (actual displacement angle) ofthe intake valve (exhaust valve) based upon output signals of a crankangle sensor 44 and a cam angle sensor 45 and also calculates targetvalve timing (target displacement angle) of the intake valve (exhaustvalve) based upon outputs of various sensors such as an intake pressuresensor and a water temperature sensor for detecting an engine operatingcondition. In addition, the ECU 43 feedback-controls (orfeedforward-controls) a control current value of the hydraulic controlvalve 21 in the variable valve timing adjusting mechanism 11 so that theactual valve timing is equal to the target valve timing. Thereby, thehydraulic pressures in the advance chamber 18 and the retard chamber 19are controlled to rotate the vane rotor 14 relative to the housing 12,causing a displacement angle of the cam shaft to be varied for makingthe actual valve timing be equal to the target valve timing.

Here, when the intake valve or the exhaust valve is opened/closed duringengine operating, the torque fluctuation the cam shaft receives from theintake valve or the exhaust valve is transmitted to the vane rotor 14,causing the torque fluctuation in the retard direction and in theadvance direction to be exerted on the vane rotor 14. In consequence,when the vane rotor 14 is subjected to the torque fluctuation in theretard direction, the operating oil in the advance chamber 18 receivesthe pressure to be pushed out of the advance chamber 18 and on the otherhand, when the vane rotor 14 is subjected to the torque fluctuation inthe advance directions the operating oil in the retard chamber 19receives the pressure to be pushed out of the retard chamber 19.Therefore, in a low-rotation region where a discharge hydraulic pressureof the oil pump 27 as a hydraulic supply source is low, without theone-way valves 30 and 31 even if the hydraulic pressure is designed tobe supplied to the advance chamber 18 to advance a displacement angle ofthe cam shaft, as shown in a dotted line of FIG. 3, the vane rotor 14 ispushed back in the retard direction due to the torque fluctuation,raising the problem that the response time until the vane rotor 14reaches a target displacement angle is longer.

On the other hand, in the present embodiment, the one-way valves 30 and31 are disposed in the hydraulic supply oil passage 28 of the advancechamber 18 and the hydraulic supply oil passage 29 of the retard chamber19 for preventing reverse flow of the operating oil from the respectivechambers 18 and 19. Further, the drain oil passage 32 and 33 forbypassing the one-way valves 30 and 31 respectively are disposed inparallel in the hydraulic supply oil passages 28 and 29 of therespective chambers 18 and 19, and drain switching valves 34 and 35 aredisposed in the drain oil passages 32 and 33 respectively. As a result,as shown in FIG. 2( a), (b) and (c), the hydraulic pressures in thechambers 18 and 19 respectively are controlled in response to a retardoperation, a holding operation and an advance operation as follows.

[Retard Operation]

As shown in FIG. 2( a), during retard operating where the actual valvetiming is relatively quickly retarded toward the target valve timing inthe retard side, the hydraulic pressure is added to the drain switchingvalve 34 in the advance chamber 18 from the hydraulic control valve 21to open the drain switching valve 34 in the advance chamber 18, creatingthe state where the one-way valve 30 in the advance chamber 18 does notfunction. Further, the hydraulic supply to the drain switching valve 35in the retard chamber 19 is stopped to close the drain switching valve35 in the retard chamber 19, creating the state where the one-way valve31 in the retard chamber 19 functions. In consequence, even at a lowhydraulic pressure, upon occurrence of the torque fluctuation in theadvance direction of the vane rotor 14, the reverse flow of oil from theretard chamber 19 is prevented with the one-way valve 31, whileefficiently supplying the hydraulic pressure to the retard chamber 19,thereby improving the retard response characteristic.

[Intermediate Holding]

As shown in FIG. 2( b), during intermediate holding of holding theactual valve timing to the target valve timing, the hydraulic supply toboth of the drain switching valves 34 and 35 in the advance chamber 18and in the retard chamber 19 is stopped to close the drain switchingvalves 34 and 35, creating the state where the one-way valves 30 and 31in the advance chamber 18 and in the retard chamber 19 function. In thisstate, even if the torque fluctuations in the retard direction and inthe advance direction are applied to the vane rotor 14 due to the torquefluctuations which the cam shaft receives from the intake valve or theexhaust valve, the reverse flow of oil from both of the advance chamber18 and the retard chamber 19 is prevented with the one-way valve 31 toprevent reduction in the hydraulic pressures holding the vane 17 fromboth side thereof thereby improving the holding stability. It should benoted that in a case of performing a relatively gentle advance/retardoperation, for improving the holding stability, the drain switchingvalves 34 and 35 in both of the advance chamber 18 and the retardchamber 19 are closed. As a result, the one-way valves 30 and 31 in bothof the advance chamber 18 and the retard chamber 19 are made to be in anactivating state.

[Advance Operation]

As shown in FIG. 2( c), during advance operating where the actual valvetiming is relatively quickly advanced toward the target valve timing inthe advance side, the hydraulic pressure supply to the drain switchingvalve 34 in the advance chamber 18 is stopped to close the drainswitching valve 34 in the advance chamber 18, causing the state wherethe one-way valve 30 in the advance chamber 18 functions. Further, thehydraulic pressure from the hydraulic control valve 21 is applied to thedrain switching valve 35 in the retard chamber 19 is applied to open thedrain switching valve 35 in the retard chamber 19, creating the statewhere the one-way valve 31 in the retard chamber 19 does not function.In consequence, even at a low hydraulic pressure, the reverse flow ofoil from the advance chamber 18 upon occurrence of the torquefluctuation in the retard direction of the vane rotor 14 is preventedwith the one-way valve 30, while efficiently supplying the hydraulicpressure to the advance chamber 187 thereby improving the advanceresponse characteristic.

Next, the response characteristic of the variable valve timing adjustingmechanism 11 (hereinafter referred to as “VCT response characteristic”)will be explained with reference to FIG. 4. FIG. 4 shows one example ofa VCT response characteristic obtained by measuring a relation between acontrol current value of the hydraulic control valve 21 (hereinafter,referred to as “OCV current value”) and a response speed of the variablevalve timing adjusting mechanism 11 (hereinafter, referred to as “VCTresponse speed”).

In the present embodiment, since the one-way valves 30 and 31 and thedrain switching valves 34 and 35 are disposed in both of the advancechamber 18 and the retard chamber 19, a VCT response speed does notchange linearly to a change of an OCV current value and opening/closingof the drain switching valves 34 and 35 is switched, causing the VCTspeed to rapidly change at two locations. In the VCT responsecharacteristic of FIG. 4, the rapidly changing point of the VCT responsespeed at the retard side is a point where the drain switching valve 34in the advance chamber 18 switches from closing state to opening state,and the rapidly changing point of the VCT response speed at the advanceside is a point where the drain switching valve 35 in the retard chamber19 switches from closing state to opening state. When an OCV currentvalue at the rapidly changing point of the VCT response speed islearned, it is possible to further improve the control characteristic ina region near where the opening and the closing of the drain switchingvalves 34 and 35 are switched.

In detail, the VCT response characteristic will be learned as follows.

An OCV current value at the time of holding an actual displacement angle(hereinafter, referred to as “VCT displacement angle”) of the variablevalve timing adjusting mechanism 11 at an intermediate holding mode at atarget displacement angle is learned as a holding current value. Thelearned OCV current value is in advance stored in a rewritable,involatile memory such as a backup RAM of ECU 43. In regard to thelearning of the holding current value, if a predetermined holdingcurrent learning condition is established for each execution of theintermediate holding mode, the holding current learning value may beupdated at each time or the learning frequency of the holding currentvalue is made smaller than that of the condition establishment. Inaddition, the holding current value may be learned for each region ofthe target displacement angle (or for each engine operating region) orone holding current value in common in all the target displacementangles (or all the engine operating regions) may be learned.

Further, in a case of learning a rapidly changing point of the VCTresponse speed at the retard side, as shown in FIG. 5, an OCV currentvalue is reduced by a predetermined current value (for example, 0.05 A)from a holding current learning value for each predetermined time andthe process of measuring a VCT displacement angle changing amount ΔVCTtoward the retard side is repeated. In addition, when the VCTdisplacement angle changing amount ΔVCT toward the retard side exceeds apredetermined value K1 it is determined that the VCT response speed hasrapidly changed toward the retard side, the OCV current valueimmediately before the VCT displacement angle changing amount ΔVCTexceeds the predetermined value K1 is stored as a preliminary learningvalue of the OCV current value at the rapidly changing point of the VCTresponse speed at the retard side. In the present embodiment, thepreliminary learning value of the OCV current value at the rapidlychanging point of the VCT response speed at the retard side is stored asa deviation ΔOCV between the OCV current value and the holding currentlearning value.

As described above, after the first learning at the rapidly changingpoint of the VCT response speed at the retard side is roughly carriedout, the second learning at the rapidly changing point of the VCTresponse speed at the retard side is finely carried out as follows.First, the OCV current value (first preliminary learning value)immediately before the VCT displacement angle changing amount ΔVCTdetected at the first retard-side rapidly changing point learningexceeds the predetermined value K1 is set to an initial current value atthe second retard-side rapidly changing point learning. Further, the OCVcurrent value is reduced at every predetermined time by a predeterminedcurrent value (for example, 0.01 A) finer than at the first retard-siderapidly changing point learning to repeat the process of measuring theVCT displacement angle changing amount ΔVCT toward the retard side. Inaddition, when the VCT displacement angle changing amount ΔVCT towardthe retard side exceeds the predetermined value K1, it is determinedthat the VCT response speed has rapidly changed toward the retard side.Then, an OCV current value at a point when the VCT displacement anglechanging amount ΔVCT exceeds the predetermined value K1 is stored as afinal learning value of the OCV current value at the rapidly changingpoint of the VCT response speed at the retard side. In the presentembodiment, even in the second retard-side rapidly changing pointlearning, an OCV current value at the rapidly changing point of the VCTresponse speed at the retard side is, as shown in FIG. 7, learned by adeviation ΔOCV between the OCV current value and the holding currentlearning value.

On the other hand, the learning of a rapidly changing point of a VCTresponse speed at an advance side is also performed as the describedabove. First, as shown in FIG. 8, the OCV current value is increased bya predetermined current value (for example, 0.02 A) for eachpredetermined time from the holding current value. In addition, theprocess of measuring a VCT displacement angle changing amount ΔVCTtoward the advance side is repeated. Further, when the VCT displacementangle changing amount ΔVCT toward the advance side exceeds apredetermined value K3, it is determined that the VCT response speed hasrapidly changed toward the advance side. Then, the OCV current valueimmediately before the VCT displacement angle changing amount ΔVCTexceeds the predetermined value K3 is stored as a preliminary learningvalue of the OCV current value at the rapidly changing point of the VCTresponse speed at the advance side. In the present embodiment, thepreliminary learning value of the OCV current value at the rapidlychanging point of the VCT response speed at the advance side is storedas a deviation ΔOCV between the OCV current value and the holdingcurrent learning value.

As described above, after the first learning at the rapidly changingpoint of the VCT response speed at the advance side is roughly carriedout, the second learning at the rapidly changing point of the VCTresponse speed at the advance side is finely carried out as follows.First, the OCV current value (first preliminary learning value)immediately before the VCT displacement angle changing amount ΔVCTdetected at the first advance-side rapidly changing point learningexceeds the predetermined value K3 is set to an initial current value atthe second advance-side rapidly changing point learning. Further, theOCV current value is increased at every predetermined time by apredetermined current value (for example, 0.05 A) finer than at thefirst advance-side rapidly changing point learning to repeat the processof measuring the VCT displacement angle changing amount ΔVCT toward theadvance side, In addition, when the VCT displacement angle changingamount ΔVCT toward the advance side exceeds the predetermined value K3,it is determined that the VCT response speed has rapidly changed towardthe advance side. Then, the OCV current value at a point when the VCTdisplacement angle changing amount ΔVCT exceeds the predetermined valueK3 is stored as a final learning value of the OCV current value at therapidly changing point of the VCT response speed at the advance side. Inthe present embodiment, even in the second advance-side rapidly changingpoint learning, the OCV current value at the rapidly changing point ofthe VCT response speed at the advance side is, as shown in FIG. 10,learned by a deviation ΔOCV between the OCV current value and theholding current learning value.

However, when a target displacement angle at a normal control time isnear the maximum retard position, as the rapidly changing point of theVCT response speed at the advance side is to be learned, it is requiredto advance an actual displacement angle over the target displacementangle. Therefore, a combustion condition of the engine possiblydeteriorates.

For coping with this problem, in the present embodiment, as shown inFIG. 11, in an operating region where the target displacement angle atthe normal control time is advanced to more than a predetermined value(for example, 40° CA), the VCT response characteristic is designed to belearned. In this way, as compared to a case of learning the VCT responsecharacteristic in an operating region where the target displacementangle at the normal control time is advanced only to less than apredetermined value (for example, 20° CA), it is possible to detect thelarger VCT displacement angle changing amount ΔVCT. As a result, ahighly accurate VCT response characteristic can be learned.

In addition, in the present embodiment, as shown in FIG. 12, a targetdisplacement angle at the time of learning a VCT response characteristicis to be set to approximately a half of the target displacement angle atthe normal control time. In this way, response characteristics in boththe directions of the retard side and the advance side can besubstantially equally learned and it is also prevented that an actualdisplacement angle exceeds an upper limit displacement angle at the timeof learning the response characteristic at the advance side. Thereby,the problem due to an excessive advance can be prevented.

As shown in FIG. 13, however, when a VCT displacement is changed at thetime of learning the VCT response characteristic, the engine torquepossibly changes. When the engine torque changes largely, it gives adriver a strange feeling.

For coping with this problem, in the present embodiment, the VCTresponse characteristic is designed to be learned in an operating regionwhere a change of the engine torque to that of the VCT displacementangle is small. In this way, since the change of the engine torque dueto the change of the VCT response characteristic at the time of learningthe VCT response characteristic is made small, the VCT responsecharacteristic can be learned without nearly giving a driver a strangefeeling.

In addition, before completing the learning of the VCT responsecharacteristic, a point where the VCT response speed rapidly changes isunclear. Therefore, when the OCV current value is controlled in thevicinity of the rapidly changing point of the VCT responsecharacteristic, the VCT response speed rapidly changes unexpectedly,thus possibly generating overshoot or undershoot of the VCT displacementangle.

For coping with this problem, as shown in FIG. 14, a control prohibitionregion is set in the vicinity of the rapidly changing point of the VCTresponse speed at each of the advance side and the retard side beforecompleting the learning of the VCT response characteristic, inconsideration of a range of manufacturing variations on a basis of adesign central value of the rapidly changing point of the VCT responsespeed at each of the advance side and the retard side. In consequence,it is prohibited to control the OCV current value in the vicinity of therapidly changing point of the VCT response speed. In addition, the OCVcurrent value is feedback-controlled in an intermediate regionsandwiched by the two control prohibition regions so that a deviationbetween the VCT displacement angle and the target displacement angle ismade small. Further, then OCV current value is feedforward-controlled atan region of a further advance side from the control prohibition regionat the advance side and at an region of a further retard side from thecontrol prohibition region at the retard side, thereby increasing theVCT response speed.

On the other hand, as shown in FIG. 15, the two control prohibitionregions are eliminated after completing the learning of a VCT responsecharacteristic. In addition, the OCV current value isfeedback-controlled in an region between the OCV current learning valueof the rapidly changing point of the VCT response speed at the advanceside and the OCV current learning value of the rapidly changing point ofthe VCT response speed at the retard side so that a deviation betweenthe VCT displacement angle and the target displacement angle is madesmall. Further, the OCV current value is feedforward-controlled in aregion outside of the feedback control region, thereby increasing theVCT response speed.

The learning processing of the aforementioned VCT responsecharacteristic is executed according to each routine of FIGS. 16 to 20by ECU 43. Hereinafter, the processing content of each routine will beexplained.

[Determination Routine of a Learning Execution Condition for a VCTResponse Characteristic]

A determination routine of a learning execution condition for a VCTresponse characteristic in FIG. 16 is executed in a predetermined periodduring engine operating. When the present routine is activated, first atstep 101, an engine operating condition such as an engine rotationalspeed, an intake pressure and a cooling water temperature are detected.At next step 102, it is determined whether or not a VCT controlexecution condition is established depending on whether or not thedetected engine operating condition is within a VCT control executionregion. When the VCT control execution condition is not established, thepresent routine ends as it is, and when the VCT control executioncondition is established, the process goes to step 103, wherein it isdetermined whether or not the learning of a holding current value iscompleted.

When it is determined at step 103 that the learning of the holdingcurrent value is not completed yet, the present routine ends as it is,and when it is determined at step 103 that the learning of the holdingcurrent value is already completed, the process goes to step 104,wherein it is determined whether or not the learning of the rapidlychanging point of the VCT response speed at the retard side iscompleted. When it is determined that the learning of the rapidlychanging point of the VCT response speed at the retard side is notcompleted yet, the process goes to step 105, wherein it is determinedwhether or not the present engine operating condition (engine rotationalspeed, intake pressure and the like) is within a VCT responsecharacteristic learning region shown in FIG. 11.

When it is determined at step 105 that the present engine operatingcondition is not within the VCT response characteristic learning region,the present routine ends as it is. When it is determined that thepresent engine operating condition is within the VCT responsecharacteristic learning region, the process goes to step 106, wherein itis determined whether or not an actual displacement angle is more than alower limit value. Here, the lower limit value is set to a displacementangle required for preventing a problem such as a combustiondeterioration caused by a learning operation (retard operation) of therapidly changing point of the VCT response speed at the retard side.

When it is determined at step 106 that the actual displacement angle isless than the lower limit value, it is determined that the learningcondition in the rapidly changing point at the retard side is notestablished, the present routine ends as it is. When it is determined atstep 106 that the actual displacement angle is more than the lower limitvalue, it is determined that the learning condition in the rapidlychanging point at the retard side is established, and the process goesto step 107. Therein a learning flag of the rapidly changing point atthe retard side XVCTLRNRET is set to “1” which means a learningcondition establishment of the rapidly changing point at the retardside, and the present routine ends.

On the other hand, when it is determined at step 104 that the learningof the rapidly changing point of the VCT response speed at the retardside is completed, the process goes to step 108, wherein it isdetermined whether or not the learning of the rapidly changing point ofthe VCT response speed at the advance side is completed. When thelearning of the rapidly changing point of the VCT response speed at theadvance side is completed, the present routine ends as it is. When thelearning of the rapidly changing point of the VCT response speed at theadvance side is not completed, the process goes to step 109, wherein itis determined whether or not the present engine operating condition(engine rotational speed, intake pressure and the like) is within theVCT response characteristic learning region shown in FIG. 11.

When it is determined at step 109 that the present engine operatingcondition is not within the VCT response characteristic learning region,the present routine ends as it is. When it is determined that thepresent engine operating condition is within the VCT responsecharacteristic learning region, the process goes to step 110, wherein itis determined whether or not an actual displacement angle is less thanan upper limit value. Here, the upper limit value is set to adisplacement angle required for preventing a problem such as acombustion deterioration caused by a learning operation (advanceoperation) of the rapidly changing point of the VCT response speed atthe advance side.

When it is determined at step 110 that the actual displacement angle ismore than the upper limit value, it is determined that the learningcondition in the rapidly changing point at the advance side is notestablished, the present routine ends as it is. When it is determined atstep 110 that the actual displacement angle is less than the upper limitvalue, it is determined that the learning condition in the rapidlychanging point at the advance side is established, and the process goesto step 111. Therein a learning flag of the rapidly changing point atthe advance side XVCTLRNADV is set to “1” which means a learningcondition establishment of the rapidly changing point at the advanceside, and the present routine ends.

[Learning Routine for a VCT Response Characteristic]

A learning routine for a VCT response characteristic in FIGS. 17 and 18is executed in a predetermined period during engine operating. When thepresent routine is activated, first at step 201, an engine operatingcondition such as an engine rotational speed, an intake pressure and acooling water temperature is detected. At next step 202, it isdetermined whether or not the learning flag of the rapidly changingpoint at the retard side XVCTLRNRET is set to “1” which means thelearning condition establishment of the rapidly changing point at theretard side. When the learning flag is set to “1”, the OCV current valueof the rapidly changing point of the VCT response speed at the retardside is learned as below.

First, at step 203 the OCV current value is set to the holding currentlearning value and at next step 204, after setting the OCV currentvalue, it is determined whether or not a predetermined time T2 haselapsed. When the answer is “No”, the process goes to step 211. When theanswer is “Yes”, the process goes to step 205, wherein it is determinedwhether or not the first learning of the rapidly changing point at theretard side (the first learning of the rapidly changing point of the VCTresponse speed at the retard side) is completed. As a result, when it isdetermined that the first learning of the rapidly changing point at theretard side is not completed yet, the process goes to step 207, whereina value C1 is calculated by subtracting a predetermined current value C2(C2=0.05 A) from the holding current value learning value. When it isdetermined that the first learning of the rapidly changing point at theretard side is completed, the process goes to step 206, wherein aninitial current value for the second learning at the retard side is setto the C1 and also a current value (for example, 0.01 A) smaller than atthe first learning of the rapidly changing point at the retard side isset to a predetermined current value C2.

Thereafter, the process goes to step 208, wherein it is determinedwhether or not the OCV current value is updated for the first time. Whenit is updated for the first time, the process goes to step 210, whereinthe OCV current value of this time is set to C1 (=holding currentvalue−C2). When it is not updated for the first time, the process goesto step 209, wherein a value which is made by subtracting apredetermined current value C2 from the previous OCV current value isset to the OCV current value of this time.

By the processing of steps 203 to 210 as described above, in the firstlearning of the rapidly changing point at the retard side (the firstlearning of the rapidly changing point of the VCT response speed at theretard side), as shown in FIG. 5, the process of reducing the OCVcurrent value by the predetermined current value C2 (for example, 0.05A) from the holding current learning value at every predetermined timeis repeated. In the second learning of the rapidly changing point at theretard side (the second learning of the rapidly changing point of theVCT response speed at the retard side), as shown in FIG. 6, the processof reducing the OCV current value by the predetermined current value C2(for example, 0.01 A) from the initial current value for the secondlearning at the retard side (preliminary learning value by the firstlearning of the rapidly changing point at the retard side) at everypredetermined time is repeated. Here, the initial current value for thesecond learning at the retard side is an OCV current value immediatelybefore an absolute value of the VCT displacement angle changing amountΔVCT detected at the first learning of the rapidly changing point at theretard side exceeds the predetermined value K1 and is set at step 218 tobe described later.

As described above, after setting the OCV current value, the processgoes to step 211, wherein it is determined whether or not apredetermined time T1 has elapsed after setting the OCV current value.When the answer is “No”, the present routine ends as it is. When theanswer is “Yes”, the process goes to step 212, wherein the presentdisplacement angle is set to a VCT old. Thereafter, the process goes tostep 213, wherein it is determined whether or not a predetermined timeT2 has elapsed after setting the OCV current value. When the answer is“No”, the present routine ends as it is. When the answer is “Yes”, theprocess goes to step 214, and a value which is made by subtracting theVCT old from the present VCT displacement angle is calculated as a VCTdisplacement angle changing amount ΔVCT for ΔT time (predetermined timefrom T1 to T2). In addition, the VCT displacement angle changing amountΔVCT is stored in the corresponding memory area of a memory in ECU 43.

ΔVCT=VCT displacement angle−VCT old.

Thereafter, the process goes to step 215, wherein it is determinedwhether or not an absolute value of the VCT displacement angle changingamount ΔVCT is more than a predetermined value K1. When the absolutevalue of the VCT displacement angle changing amount ΔVCT is less thanthe predetermined value K1, it is determined that the VCT response speeddoes not rapidly change yet, and the present routine ends as it is.Thereafter, at a point where the absolute value of the VCT displacementangle changing amount ΔVCT is more than the predetermined value K1, itis determined that the VCT response speed has changed rapidly, and theprocess goes to step 216, wherein it is determined whether or not thefirst learning of the rapidly changing point at the retard side iscompleted. As a result, when the first learning of the rapidly changingpoint at the retard side is not yet completed, the process goes to step218. (1) Therein the previous OCV current value is determined to thepreliminary learning value by the first learning of the rapidly changingpoint at the retard side, which is stored as the initial current valuefor the second learning at the retard side. Further, it is determinedthat the first learning of the rapidly changing point at the retard sideis completed.

In addition, when it is determined at step 216 that the first learningof the rapidly changing point at the retard side is completed, theprocess goes to step 217, wherein (1) the present OCV current value isstored in a rewritable, involatile memory such as a backup RAM of ECU 43as a final learning value of the OCV current value of the rapidlychanging point of the VCT response speed at the retard side. Further, itis determined that the second learning of the rapidly changing point atthe retard side is completed.

On the other hand, when it is determined at step 202 that the learningflag of the rapidly changing point at the retard side XVCTLRNRET is setto “0” which means that the learning condition of the rapidly changingpoint at the retard side is not established, the process goes to step220 in FIG. 18. Therein it is determined whether or not the learningflag of the rapidly changing point at the advance side XVCTLRNADV is setto “1” which means that the learning condition of the rapidly changingpoint at the advance side is established. When the learning flag of therapidly changing point at the advance side XVCTLRNADV is not set to “1”,the present routine ends as it is and when the learning flag is set to“1”, the OCV current value of the rapidly changing point at the advanceside is learned as follows.

First, at step 221 the OCV current value is set to the holding currentlearning value and at next step 222, it is determined whether or not apredetermined time T2 has elapsed after setting the OCV current value.When the answer is “No”, the process goes to the process at step 229.When the answer is “Yes”, the process goes to step 223, wherein it isdetermined whether or not the first learning of the rapidly changingpoint at the advance side (the first learning of the rapidly changingpoint of the VCT response speed at the advance side) is completed. As aresult, when it is determined that the first learning of the rapidlychanging point at the advance side is not completed yet, the processgoes to step 225, wherein a value C3 is calculated by adding apredetermined current value C4 (for example, C4=0.02 A) to the holdingcurrent value learning value. When it is determined that the firstlearning of the rapidly changing point at the advance side is completed,the process goes to step 224, wherein then initial current value for thesecond learning at the advance side is set to the value C3 and also acurrent value (0.05 A) smaller than at the first learning of the rapidlychanging point at the advance side is set to the predetermined currentvalue C4.

Thereafter, the process goes to step 226, wherein it is determinedwhether or not the OCV current value is updated for the first time. Whenit is updated for the first time the process goes to step 228, whereinthe OCV current value of this time is set to C3 (=holding currentlearning value+C4). When it is not updated for the first time, theprocess goes to step 227, wherein a value which is made by adding thepredetermined current value C4 to the previous OCV current value is setto the OCV current value of this time.

By the processing of steps 221 to 228 as described above, in the firstlearning of the rapidly changing point at the advance side (the firstlearning of the rapidly changing point of the VCT response speed at theadvance side), as shown in FIG. 8, the process of increasing the OCVcurrent value by the predetermined current value C4 (for example, 0.02A) from the holding current learning value at every predetermined timeis repeated. In the second learning of the rapidly changing point at theadvance side (the second learning of the rapidly changing point of theVCT response speed at the advance side), as shown in FIG. 9, the processof increasing the OCV current value by the predetermined current valueC4 (for example, 0.05 A) from the initial current value for the secondlearning at the advance side (preliminary learning value by the firstlearning of the rapidly changing point at the advance side) at everypredetermined time is repeated. Here, the initial current value for thesecond learning at the advance side is an OCV current value immediatelybefore an absolute value of the VCT displacement angle changing amountΔVCT detected at the first learning of the rapidly changing point at theadvance side exceeds the predetermined value K3 and is set at step 236to be described later.

As described above, after setting the OCV current value, the processgoes to step 229, wherein it is determined whether or not apredetermined time T1 has elapsed after setting the OCV current value.When the answer is “No”, the present routine ends as it is. When theanswer is “Yes” the process goes to step 230, wherein the presentdisplacement angle is set to a VCTold. Thereafter, the process goes tostep 231, wherein it is determined whether or not a predetermined timeT2 has elapsed after setting the OCV current value. When the answer is“No”, the present routine ends as it is. When the answer is “Yes”, theprocess goes to step 232, and a value which is made by subtracting theVCT old from the present VCT displacement angle is calculated as a VCTdisplacement angle changing amount ΔVCT for ΔT time (predetermined timefrom T1 to T2). In addition, the VCT displacement angle changing amountΔVCT is stored in the corresponding memory region of a memory in ECU 43.

ΔVCT=VCT displacement angle−VCTold.

On this occasion, a deviation ΔVCT between the OCV current value and theholding current learning value is used as a data of the OCV currentvalue. In consequence, there is produced a table of the VCT displacementangle changing amount ΔVCT using the deviation ΔVCT between the OCVcurrent value and the holding current learning value as a parameter.

Thereafter, the process goes to step 233, wherein it is determinedwhether or not an absolute value of the VCT displacement angle changingamount ΔVCT is more than the predetermined value K3. When the absolutevalue of the VCT displacement angle changing amount ΔVCT is less thanthe predetermined value K3, it is determined that the VCT response speeddoes not rapidly change yet, and the present routine ends as it is.Thereafter, at a point where the absolute value of the VCT displacementangle changing amount ΔVCT is more than the predetermined value K3, itis determined that the VCT response speed has changed rapidly, theprocess goes to step 234, wherein it is determined whether or not thefirst learning of the rapidly changing point at the advance side iscompleted. As a result, when the first learning of the rapidly changingpoint at the advance side is not yet completed, the process goes to step236. (1) Therein the previous OCV current value is determined as apreliminary learning value by the first learning of the rapidly changingpoint at the advance side, which is stored as an initial current valuefor the second learning at the advance side. Further, it is determinedthat the first learning of the rapidly changing point at the advanceside is completed.

In addition, when it is determined at step 234 that the first learningof the rapidly changing point at the advance side is completed, theprocess goes to step 235, wherein (1) the present OCV current value isstored in a rewritable, involatile memory such as a backup RAM of ECU 43as a final learning value of the OCV current value of the rapidlychanging point of the VCT response speed at the advance side. Further,it is determined that the second learning of the rapidly changing pointat the advance side is completed.

[Control Routine for an OCV Current]

A control routine for an OCV current in FIG. 19 is executed in apredetermined period during engine operating. When the present routineis activated, first at step 301, an engine operating condition such asan engine rotational speed, an intake pressure and a cooling watertemperature is detected. At next step 302, it is determined whether ornot the learning flag of the rapidly changing point at the retard sideXVCTLRNRET is “1” or the learning flag of the rapidly changing point atthe advance side XVCTLRNADV is “1”. When one of the learning flag of therapidly changing point at the retard side XVCTLRNRET and the learningflag of the rapidly changing point at the advance side XVCTLRNADV is“1”, it is determined that the VCT response characteristic is in themiddle of being learned. In addition, the process goes to step 303,wherein a current value for learning is set to the OCV current value andthe present routine ends. This current value for learning is the OCVcurrent value in the middle of learning the VCT response characteristiccalculated at steps 209, 210, 227 and 228 in the learning routine of theVCT response characteristic in FIGS. 17 and 18

On the other hand, when both of the learning flag of the rapidlychanging point at the retard side XVCTLRNRET and the learning flag ofthe rapidly changing point at the advance side XVCTLRNADV are “0”, it isdetermined that the VCT response characteristic is during normalcontrolling. In addition, the process goes to step 304, wherein acurrent value for normal control is set to the OCV current value and thepresent routine ends. This current value for normal control is an OCVcurrent value calculated at normal controlling in a calculation routineof a current value for normal control in FIG. 20 to be described later.

[Calculation Routine of a Current Value for Normal Control]

A calculation routine for a current value for normal control in FIG. 20is executed in a predetermined period during engine operating. When thepresent routine is activated, first at step 401, an engine operatingcondition such as an engine rotational speed, an intake pressure and acooling water temperature is detected. At next step 402, it isdetermined whether or not the learning of the rapidly changing point ofthe VCT response speed at the retard side is completed. When thelearning of the rapidly changing point of the VCT response speed at theretard side is not completed yet, the process goes to step 404. Therein,as shown in FIG. 14, a lower limit current value in the feedback controlregion is set to a predetermined value C5 and also an upper limitcurrent value in the feedforward control region at the retard side isset to a predetermined value C6.

On the other hand, when it is determined at step 402 that the learningof the rapidly changing point of the VCT response speed at the retardside is completed, the process goes to step 403. Therein the lower limitcurrent value in the feedback control region and the upper limit currentvalue in the feedforward control region at the retard side both are setto the OCV current learning value in the rapidly changing point of theVCT response speed at the retard side.

Thereafter, the process goes to step 405, and it is determined whetheror not the learning of the rapidly changing point of the VCT responsespeed at the advance side is completed. When the learning of the rapidlychanging point of the VCT response speed at the advance side is notcompleted yet, the process goes to step 406. Therein, as shown in FIG.14, the upper limit current value in the feedback control region is setto a predetermined value C7 and also the lower limit current value inthe feedforward control region at the advance side is set to apredetermined value C8.

In this case, the upper and lower limit current values C7 and C5 in thefeedback control region and the upper and lower limit current values C6and C8 in the feedforward control region are set in consideration of arange of the manufacturing variations on a basis of the design centralvalue in the rapidly changing point of the VCT response speed at each ofthe advance side and the retard side. As a result, the range of themanufacturing variations in the rapidly changing point of the VCTresponse speed is within the control prohibition regions (C6 to C5 andC7 to C8) provided between the feedback control region and thefeedforward control region.

On the other hand, when it is determined at step 405 that the learningof the rapidly changing point of the VCT response speed at the advanceside is completed, the process goes to step 406. Therein the upper limitcurrent value in the feedback control region and the lower limit currentvalue in the feedforward control region at the advance side both are setto the OCV current learning value in the rapidly changing point of theVCT response speed at the advance side.

Thereafter, the process goes to step 408, wherein the OCV current valueis calculated in accordance with the deviation between the VCTdisplacement angle and the target displacement angle, within the upperand lower limit ranges in each of the feedback control region and thefeedback control region.

[Calculation Routine for a Target Displacement Angle]

A calculation routine for a target displacement angle in FIG. 21 isexecuted in a predetermined period during engine operating. When thepresent routine is activated, first at step 501, an engine operatingcondition such as an engine rotational speed, an intake pressure and acooling water temperature is detected. At next step S502, it isdetermined whether or not the learning flag of the rapidly changingpoint at the retard side XVCTLRNRET is “1” or the learning flag of therapidly changing point at the advance side XVCTLRNADV is “1”. When oneof the learning flag of the rapidly changing point at the retard sideXVCTLRNRET and the learning flag of the rapidly changing point at theadvance side XVCTLRNADV is “1”, it is determined that the VCT responsecharacteristic is in the middle of being learned. In addition, theprocess goes to step S503, wherein the target displacement angle is setto a predetermined value of approximately a half of the targetdisplacement angle at normal controlling.

On the other hand, when both of the learning flag of the rapidlychanging point at the retard side XVCTLRNRET and the learning flag ofthe rapidly changing point at the advance side XVCTLRNADV are “0”, it isdetermined that the VCT is in the middle of the normal controlling. Inaddition, the process goes to step 504, wherein by referring to a map oftarget displacement angles in the middle of the normal controlling shownin FIG. 11, the target displacement angle is set to a targetdisplacement angle in accordance with the present engine operatingcondition (engine rotational speed, intake pressure and the like).

According to the present embodiment as described above, in the VCTresponse characteristic in FIG. 4, the OCV current values in the rapidlychanging point of the VCT response speed at the retard side and in therapidly changing point of the VCT response speed at the advance side areto be learned. Therefore, use of the learning value causes the variablevalve timing control (OCV current control) to be realized inconsideration of the manufacturing variations of the variable valvetiming adjusting mechanism 11 and the hydraulic control valve 21. Indetail, when the OCV current values in the rapidly changing point of theVCT response speed at the retard side and in the rapidly changing pointof the VCT response speed at the advance side are learned, it ispossible to eliminate or reduce the control prohibition region in thevicinity of the rapidly changing point of each of the VCT responsespeeds (refer to FIG. 14). Thereby, the feedback control region or thefeedforward control region can be enlarged by the corresponding amountand the control characteristic in the region of the rapidly changingpoint of the VCT response speed can be improved by the learning value.

It should be noted that the learning of the VCT response characteristicis not limited to the learning of the rapidly changing point of the VCTresponse speed, but for example, the drain switching valve 34 or 35 ineither one of the advance chamber 18 and the retard chamber 19 may beopened to learn a relation between the OCV current value and the VCTresponse speed in a region where either one of the one-way valve 30 or31 does not function. Alternatively, the drain switching valves 34 and35 in both of the advance chamber 18 and the retard chamber 19 may beclosed to learn a relation between the OCV current value and the VCTresponse speed in a region where both of the one-way valves 30 and 31effectively function. Here, the region where either one of the one-wayvalve 30 or 31 does not function is a region of performing a relativelyrapid advance/retard operation (in the present embodiment, this regionis set to the feedforward control region). Further, the region whereboth of the one-way valves 30 and 31 effectively function is a region ofperforming a relatively gentle advance/retard operation and a region atintermediate holding (in the present embodiment, this region is set tothe feedback control region). In this way, when the VCT responsecharacteristic in the region other than the rapidly changing point ofthe VCT response speed is learned, the variations of the VCT responsecharacteristic due to the manufacturing variations in the variable valvetiming adjusting mechanism 11 or the hydraulic control valve 21 can bewidely learned and corrected. In consequence, the control characteristicin the region other than the rapidly changing point of the VCT responsespeed can be improved.

In addition, in the present embodiment, the learning value of the VCTresponse characteristic is stored in the rewritable, involatile memory.Therefore, the stored learning value of the VCT response characteristiccan be held even at engine stopping, thus providing an advantage ofbeing capable of accurately controlling the OCV current value by usingthe learning value of the VCT current value immediately after the engineis next started.

It should be noted that in the present embodiment, the present inventionis applied to the variable valve timing adjusting mechanism shown inFIG. 1, but is not limited to this and for example, may be also appliedto a variable valve timing adjusting mechanism shown in FIG. 22.

The variable valve timing adjusting mechanism shown in FIG. 22 differsin the following respect form that of FIG. 1. It should be noted thatcomponents in FIG. 22 identical to those in FIG. 1 are referred to asidentical numerals.

The variable valve timing adjusting mechanism shown in FIG. 1 isstructured to be provided with two valves composed of the valve ofswitching the oil passages for the advance/retard hydraulic controlfunction and the valve of switching the oil passages for the drainswitching control function. On the other hand, the variable valve timingadjusting mechanism shown in FIG. 22 is structured in such a manner asto carry out the advance/retard hydraulic control function and the drainswitching control function by a single valve. In addition, therefore, itis structured in such a manner that the hydraulic supply passages 28 and29 are branched between the hydraulic control valve and the one-wayvalve and are respectively communicated with the drain switching valves34 and 35.

In addition, in FIG. 1, the one-way valve and the drain switching valveare disposed in the hydraulic pressure supply passages corresponding tothe advance chamber and the retard chamber in the singlevane-accommodating chamber defined by a single vane, but in FIG. 22, theone-way valve and the drain switching valve are disposed in thehydraulic pressure supply passage corresponding to the advance chamberin one vane-accommodating chamber and also in the hydraulic pressuresupply passage corresponding to the retard chamber in the othervane-accommodating chamber.

In addition, the drain switching valves 34 and 35 may be normallyclosed-type switching valves, which are held in a closed position bysprings 41 and 42 when the hydraulic pressure is not applied thereto. Inthis case, the drain switching control valve 38 is structured to supplythe hydraulic pressure at the time of closing the drain switching valvein FIG. 1, but may be structured to stop the hydraulic pressure supplyat the time of closing the drain valve.

1-29. (canceled)
 30. A controller for a vane-type variable valve timingadjusting mechanism in which each of a plurality of vane accommodatingchambers formed in a housing is divided into an advance hydraulicchamber and a retard hydraulic chamber by a vane, a one-way valve isdisposed in each of a hydraulic supply passage of the advance hydraulicchamber and a hydraulic supply passage of the retard hydraulic chamberin at least one of the vane accommodating chambers for preventingreverse flow of operating oil from the each hydraulic chamber, a drainoil passage is disposed in parallel to the hydraulic supply passage ofthe each hydraulic chamber for bypassing the one-way valve and ahydraulic control valve for controlling a hydraulic pressure supplied tothe each hydraulic chamber includes integrally a drain switching controlfunction for opening/closing the drain oil passage of the each hydraulicchamber, wherein: response characteristic learning means is provided forlearning a response characteristic of the variable valve timingadjusting mechanism to a control current value of the hydraulic controlvalve.
 31. A controller for a vane-type variable valve timing adjustingmechanism according to claim 30, wherein. the response characteristiclearning means learns a control current value with which a responsespeed of the variable valve timing adjusting mechanism rapidly changesby switching the opening/closing of the drain oil passage, as theresponse characteristic of the variable valve timing adjustingmechanism.
 32. A controller for a vane-type variable valve timingadjusting mechanism according to claim 30, wherein: the responsecharacteristic learning means learns a relation between the controlcurrent value of the hydraulic control valve and the response speed ofthe variable valve timing adjusting mechanism in a region where thedrain oil passage in one of the advance hydraulic chamber and the retardhydraulic chamber is opened and one of the one-way valves does notfunction, as the response characteristic of the variable valve timingadjusting mechanism.
 33. A controller for a vane-type variable valvetiming adjusting mechanism according to claim 30, wherein: the responsecharacteristic learning means learns a relation between the controlcurrent value of the hydraulic control valve and the response speed ofthe variable valve timing adjusting mechanism in a region where thedrain oil passages in both of the advance hydraulic chamber and theretard hydraulic chamber are closed and both the one-way valveseffectively function, as the response characteristic of the variablevalve timing adjusting mechanism.
 34. A controller for a vane-typevariable valve timing adjusting mechanism according to claim 30, furthercomprising: holding current value learning means for learning a controlcurrent value of the hydraulic control valve at the time of holding anactual displacement angle of the variable valve timing adjustingmechanism to a target displacement angle as a holding current value,wherein: the response characteristic learning means learns a responsecharacteristic of the variable valve timing adjusting mechanism to adeviation between the holding current value learned by the holdingcurrent value learning means and the control current value of thehydraulic control valve, at the time of learning the responsecharacteristic of the variable valve timing adjusting mechanism.
 35. Acontroller for a vane-type variable valve timing adjusting mechanismaccording to claim 30, wherein: the response characteristic learningmeans learns a response characteristic of the variable valve timingadjusting mechanism in an operating region where a target displacementangle at normal controlling is advanced to more than a predeterminedvalue.
 36. A controller for a vane-type variable valve timing adjustingmechanism according to claim 30 wherein: the response characteristiclearning means sets a target displacement angle at the time of learningthe response characteristic of the variable valve timing adjustingmechanism to approximately a half of the target displacement angle atnormal controlling.
 37. A controller for a vane-type variable valvetiming adjusting mechanism according to claim 30, wherein: the responsecharacteristic learning means learns a response characteristic of thevariable valve timing adjusting mechanism in an operating region where achange of engine torque to a change of an actual displacement angle ofthe variable valve timing adjusting mechanism is small.
 38. A controllerfor a vane-type variable valve timing adjusting mechanism according toclaim 30, further comprising: a rewritable involatile memory for storinga learning value of the response characteristic of the variable valvetiming adjusting mechanism learned by the response characteristiclearning means; and current control means for correcting the controlcurrent value of the hydraulic control valve by using the learning valueof the response characteristic stored in the involatile memory duringengine operating.
 39. A controller for a vane-type variable valve timingadjusting mechanism according to claim 30, further comprising; a drainswitching valve disposed in the each drain oil passage and driven by ahydraulic pressure, wherein: the each drain oil passage is opened/closedby opening/closing the each drain switching valve by hydraulic controlof the drain switching control function of the hydraulic control valve.40. A controller for a vane-type variable valve timing adjustingmechanism in which each of a plurality of vane accommodating chambersformed in a housing is divided into an advance hydraulic chamber and aretard hydraulic chamber by a vane, the controller comprising: a firstone-way valve disposed in a hydraulic supply passage of the advancehydraulic chamber in at least one of the vane accommodating chambers forpreventing reverse flow of operating oil from the advance hydraulicchamber; a first drain oil passage bypassing the first one-way valve; asecond one-way valve disposed in a hydraulic supply passage of theretard hydraulic chamber in at least one of the vane accommodatingchambers for preventing reverse flow of operating oil from the retardhydraulic chamber; a second drain oil passage bypassing the secondone-way valve; and a hydraulic control valve for controlling thehydraulic pressure supplied to the variable valve timing adjustingmechanism, wherein: the hydraulic control valve includes integrally adrain switching control function for opening/closing the first andsecond drain oil passages, further comprising: response characteristiclearning means for learning a response characteristic of the variablevalve timing adjusting mechanism to a control current value of thehydraulic control valve.
 41. A controller for a vane-type variable valvetiming adjusting mechanism according to claim 40, wherein: the responsecharacteristic learning means learns a control current value with whicha response speed of the variable valve timing adjusting mechanismrapidly changes by switching the opening/closing of the drain oilpassage, as the response characteristic of the variable valve timingadjusting mechanism.
 42. A controller for a vane-type variable valvetiming adjusting mechanism according to claim 40, wherein: the responsecharacteristic learning means learns a relation between the controlcurrent value of the hydraulic control valve and the response speed ofthe variable valve timing adjusting mechanism in a region where thedrain oil passage in one of the advance hydraulic chamber and the retardhydraulic chamber is opened and one of the one-way valves does notfunction, as the response characteristic of the variable valve timingadjusting mechanism.
 43. A controller for a vane-type variable valvetiming adjusting mechanism according to claim 40, wherein: the responsecharacteristic learning means learns a relation between the controlcurrent value of the hydraulic control valve and the response speed ofthe variable valve timing adjusting mechanism in a region where thedrain oil passages in both of the advance hydraulic chamber and theretard hydraulic chamber are closed and both the one-way valveseffectively function, as the response characteristic of the variablevalve timing adjusting mechanism.
 44. A controller for a vane-typevariable valve timing adjusting mechanism according to claim 40, furthercomprising: holding current value learning means for learning a controlcurrent value of the hydraulic control valve at the time of holding anactual displacement angle of the variable valve timing adjustingmechanism to a target displacement angle as a holding current value,wherein: the response characteristic learning means learns a responsecharacteristic of the variable valve timing adjusting mechanism to adeviation between the holding current value learned by the holdingcurrent value learning means and the control current value of thehydraulic control valve at the time of learning the responsecharacteristic of the variable valve timing adjusting mechanism.
 45. Acontroller for a vane-type variable valve timing adjusting mechanismaccording to claim 40, wherein: the response characteristic learningmeans learns a response characteristic of the variable valve timingadjusting mechanism in an operating region where a target displacementangle at normal controlling is advanced to more than a predeterminedvalue.
 46. A controller for a vane-type variable valve timing adjustingmechanism according to claim 40, wherein; the response characteristiclearning means sets a target displacement angle at the time of learningthe response characteristic of the variable valve timing adjustingmechanism to approximately a half of the target displacement angle atnormal controlling.
 47. A controller for a vane-type variable valvetiming adjusting mechanism according to claim 40, wherein: the responsecharacteristic learning means learns a response characteristic of thevariable valve timing adjusting mechanism in an operating region where achange of engine torque to a change of an actual displacement angle ofthe variable valve timing adjusting mechanism is small.
 48. A controllerfor a vane-type variable valve timing adjusting mechanism according toclaim 40, further comprising: a rewritable, involatile memory forstoring a learning value of the response characteristic of the variablevalve timing adjusting mechanism learned by the response characteristiclearning means; and current control means for correcting the controlcurrent value of the hydraulic control valve by using the learning valueof the response characteristic stored in the involatile memory duringengine operating.
 49. A controller for a vane-type variable valve timingadjusting mechanism according to claim 40, further comprising: a firstdrain control valve disposed in the first drain oil passage and drivenby a hydraulic pressure; and a second drain control valve disposed inthe second drain oil passage and driven by a hydraulic pressure,wherein: the first drain oil passage is opened/closed by opening/closingthe first drain control valve and the second drain oil passage isopened/closed by opening/closing the second drain control valve byhydraulic control of the drain oil passage control function of thehydraulic control valve by hydraulic control of the drain oil passagecontrol function of the hydraulic control valve.
 50. A controller for avane-type variable valve timing adjusting mechanism in which each of aplurality of vane accommodating chambers formed in a housing is dividedinto an advance hydraulic chamber and a retard hydraulic chamber by avane, the controller comprising: a first one-way valve disposed in ahydraulic supply passage of the advance hydraulic chamber in at leastone of the vane accommodating chambers for preventing reverse flow ofoperating oil from the advance hydraulic chamber; a first drain controlvalve disposed in a first drain oil passage bypassing the first one-wayvalve and driven by a hydraulic pressure; a second one-way valvedisposed in a hydraulic supply passage of the retard hydraulic chamberin at least one of the vane accommodating chambers for preventingreverse flow of operating oil from the retard hydraulic chamber a seconddrain control valve disposed in a second drain oil passage bypassing thesecond one-way valve and driven by the hydraulic pressure; a firsthydraulic control valve for controlling the hydraulic pressure suppliedto the variable valve timing adjusting mechanism; and a second hydrauliccontrol valve for controlling the hydraulic pressure driving the firstand second drain control valves, wherein: a shaft of the first hydrauliccontrol valve is integral with a shaft of the second hydraulic controlvalve, further comprising: response characteristic learning means forlearning a response characteristic of the variable valve timingadjusting mechanism to a control current value for controlling thehydraulic control valve and the drain control valve.
 51. A controllerfor a vane-type variable valve timing adjusting mechanism according toclaim 50, wherein: the response characteristic learning means learns acontrol current value with which a response speed of the variable valvetiming adjusting mechanism rapidly changes by switching theopening/closing of the first drain oil passage and the second drain oilpassage, as the response characteristic of the variable valve timingadjusting mechanism.
 52. A controller for a vane-type variable valvetiming adjusting mechanism according to claim 50, wherein: the responsecharacteristic learning means learns a relation between the controlcurrent value for controlling the hydraulic control valve and the draincontrol valve, and the response speed of the variable valve timingadjusting mechanism in a region where the drain oil passage in one ofthe advance hydraulic chamber and the retard hydraulic chamber is openedand one of the one-way valves does not function, as the responsecharacteristic of the variable valve timing adjusting mechanism.
 53. Acontroller for a vane-type variable valve timing adjusting mechanismaccording to claim 50, wherein: the response characteristic Teamingmeans learns a relation between the control current value forcontrolling the first and second hydraulic control valves and theresponse speed of the variable valve timing adjusting mechanism in aregion where the drain oil passages in both of the advance hydraulicchamber and the retard hydraulic chamber are closed and both the one-wayvalves effectively function, as the response characteristic of thevariable valve timing adjusting mechanism.
 54. A controller for avane-type variable valve timing adjusting mechanism according to claim50, further comprising: holding current value learning means forlearning a control current value for controlling the first and secondhydraulic control valves at the time of holding an actual displacementangle of the variable valve timing adjusting mechanism to a targetdisplacement angle, as a holding current value, wherein: the responsecharacteristic learning means learns a response characteristic of thevariable valve timing adjusting mechanism to a deviation between theholding current value learned by the holding current value learningmeans and the control current value of the hydraulic control valve, atthe time of learning the response characteristic of the variable valvetiming adjusting mechanism.
 55. A controller for a vane-type variablevalve timing adjusting mechanism according to claim 50, wherein: theresponse characteristic learning means learns a response characteristicof the variable valve timing adjusting mechanism in an operating regionwhere a target displacement angle at normal controlling is advanced tomore than a predetermined value.
 56. A controller for a vane-typevariable valve timing adjusting mechanism according to claim 50,wherein: the response characteristic learning means sets a targetdisplacement angle at the time of learning the response characteristicof the variable valve timing adjusting mechanism to approximately a halfof the target displacement angle at normal controlling.
 57. A controllerfor a vane-type variable valve timing adjusting mechanism according toclaim 50, wherein: the response characteristic learning means learns aresponse characteristic of the variable valve timing adjusting mechanismin an operating region where a change of engine torque to a change of anactual displacement angle of the variable valve timing adjustingmechanism is small.
 58. A controller for a vane-type variable valvetiming adjusting mechanism according to claim 50, further comprising: arewritable, involatile memory for storing a learning value of theresponse characteristic of the variable valve timing adjusting mechanismlearned by the response characteristic learning means; and currentcontrol means for correcting the control current value for controllingthe first and second hydraulic control valves by using the learningvalue of the response characteristic stored in the involatile memoryduring engine operating.